This invention relates generally to imaging systems and more particularly to systems and methods for reading data from a detector.
A solid state x-ray detector includes of an array of pixels having a plurality of switches and photodiodes over which Cesium Iodide (CsI) is deposited. The CsI absorbs x-rays and converts the x-rays to light, which is detected by the photodiodes. Each photodiode, due to its construction, acts as a capacitor and stores charge. Initialization of the detector takes place prior to an x-ray exposure, when each photodiode is charged to an initial voltage. The detector is then exposed to the x-rays, which are absorbed by the CsI. The light that is emitted in proportion to a portion of the x-rays partially discharges each photodiode. After the exposure, a voltage on each photodiode is restored to the initial voltage. An amount of charge used to restore the initial voltage on the photodiode is measured, which becomes a measure of an x-ray dose integrated by a pixel during a length of the exposure.
The detector is read or alternatively scrubbed on a row-by-row basis, as controlled by the switches associated with each photodiode. Reading is performed whenever an image acquired by the detector includes exposure data or alternatively offset data. Scrubbing is similar to reading except that data acquired from scrubbing is not interesting, and is therefore discarded. Scrubbing is performed to maintain proper bias on the photodiodes during idle periods, perhaps to reduce a plurality of effects of lag, which is incomplete charge restoration of the photodiodes, or alternatively to maintain a plurality of thresholds of the switches. The thresholds may shift if the switches are kept in an “off” state for long periods, among other reasons. Scrubbing restores charge on each photodiode and the charge need not be measured. If the charge is measured, data acquired from scrubbing can be discarded.
Scrubbing is performed to keep the detector ready for use largely due to the less than ideal characteristics of amorphous silicon used to fabricate the detector.
However, scrubbing is undesirable for several reasons. Scrubbing represents non-productive overhead, uses power to perform, the dissipation of which is undesirable especially in low power applications. Scrubbing may create an access time latency before the commencement of the exposure to allow completion of the scrub prior to the start of the exposure. The time used to scrub takes away from the detector's availability.